Ultrasound: Palm Rejection Support for Protocol B TSC Drivers

The Ultrasound stylus can't work simultaneously with touch screen
driver, because Android input module can't handle events from multiple
input drivers. The solution proposed was to filter out touchscreen
driver events, this solution proved to be efficient for Touchscreen
drivers that work with multitouch protocol A, but for drivers working
with multitouch protocol B this solution was not enough to clear out
all touchscreen driver trace. This commit fixes this by 'free'ing all
mt slots allocated by the touchscreen driver before filtering out all
of touchscreen driver's events.

Change-Id: Icde80fc9e238a72dac30a46927a7863424b209a7

Signed-off-by: Rani Khoury <rkhoury@codeaurora.org>